On the BAUT forum someone asked what the solar system would be like if Jupiter had been a star to start with. In the process of answering, I figured out that the barycentre of the Sol-Jupiter system (if Jupiter was 0.08 solar masses) would be 0.3855 AU from Sol - that happens to be at pretty much the same orbital distance as Mercury.

Which got me wondering - what would happen to a planet that tried to orbit the same distance as the barycentre? In that scenario Sol could hold onto planets out to 2.12 AU so it's not impossible for there to be a planet orbiting Sol itself at a distance of 0.3855 AU. Or would EVERYTHING have to orbit the barycentre?

Remember that Jupiter tugs Mercury about as hard as it tugs the Sun, cancelling out most of the effect. A planet that tried to orbit the Sun in at the same distance as the barycenter of the Sun-Jupiter system would often find itself beneath the surface of the Sun. If Jupiter had 10x mass... I'm not sure.

Is it something that can be simulated in gravity simulator? Can it handle barycentres yet?

Gravity Simulator has always been able to handle barycenters. They are a natural consequence of n-body simulations. The default view is to lock an object to the middle of the screen, hiding the barycenter, but on the "Graphics Options" interface is a button "F" which turns into "A" if you press it, and back to "F" if you press it again. It toggles you between Absolute (default) mode and Floating (barycenter) mode.

Here's an image I made of the path of the Sun around our solar system's barycenter. This represents about 100 years. To make this, I edited the Sun's size to 0 so it would trace a thin path. Then I set it to floating mode and zoomed in. Then I photoshopped a circle the size of the Sun into the image for comparison. As you can see, the barycenter of the solar system is often beneath the surface of the Sun, but the Sun often ventures beyond the barycenter. In any case, the barycenter of the solar system is never external to the solar corona.

To make an object orbit the Sun at the distance of the barycenter of a Sun / 10xJupiter system: